Electron beam control device for use with a cathode ray tube for dynamic correction of electron beam astigmatism and defocusing



March 31, 1970 TAKEO TAKEMOTO ET AL 3,504,211

ELECTRON BEAM CONTROL DEVICE FOR USE WITH A GATHODE RAY TUBE FOR DYNAMIC CORRECTION OF ELECTRON BEAM ASTIGMATISM .AND DEFOCUSING Filed May 4, 1966 .5 Sheets-Sheet 1 INVENTORS HKE TQKEmoro "mag 072.4 Fax/HIM auzE 10774010028 BY I QI AQ A ITORNEY March 31, 1970 TAKEO TAKEMOTO ET AL 3,504,211

- ELECTRON BEAM CONTROL DEVICE FOR USE WITH A CATHODE RAY TUBE FOR DYNAMIC CORRECTION OF ELECTRON BEAM ASTIGMATISM AND DEFOCUSING Filed May 4, 1966 .5 Sheets-Sheet 2 F/G. 60 F/G 60 (a) b (d) W (e) H L n n rL M f VII-TI (a) W 9) LLJLJL (M {LILLIL INVENTORS 72x50 Tmemn MAsnmnAlL Fuusmmn BY I Q ZZ I ORNEY March 31, 1970 TAKEQ TAKEMOTO ET AL 3,504,211

ELECTRON BEAM CONTROL DEVICE FOR USE WITH A CATHODE RAY TUBE FOR DYNAMIC CORRECTION OF ELECTRON BEAMASTIGMATISM AND DEFOCUSING Filed May 4, 1966 .5 Sheets-Sheet 3 INVENTORS 71 mm fixemo'ro MR'BAMAALL Futiummh Kaunas. lbw-71:24am

A ORNEY March 31, 1970 TAKEO TAKEMOTO ET AL 3,504,211

ELECTRON BEAM CONTROL DEVICE-FOR USE WITH A CATHODE RAY TUBE FOR DYNAMIC CORRECTION OF ELECTRON BEAM ASTIGMATISM AND DEFOCUSING Filed May 4, 1966 5 Sheets-Sheet 4 INVENTORS 775/150 Tnrzamora Mnanm ma Mama Kosuxs Kmqmunn ATTORNEY United States Patent US. Cl. 313-84 9 Claims ABSTRACT OF THE DISCLOSURE A device for use with a cathode ray tube which comprises at least one electron lens for producing a four-pole field which, for example, deflects electrons inwardly toward the center of the electron beam of the tube in a direction of X-axis and outwardly away from the center of the electron beam in a direction of Y-axis perpendicular to X-axis. Astigmatism of the electron beam is reduced by adjusting the angular position of the electron lens around the electron beam and/or the polarity and intensity of the four-pole field. When a pair of lenses arranged with an angular displacement to each other of about 45 is used the astigmatism is corrected without varying the angular position of the lenses by just varying the polarity and intensity of the four-pole field of each lens.

This invention relates to an electron beam control device for use in cathode-ray tubes and more particularly to a novel electron beam control device in which an electromagnetic lens consisting of four electromagnetic poles is provided in order to correct any variation in the shape and size of beam spots due to astigmatism peculiar to the electron gun of a cathode-ray tube and astigmatism of the deflecting yoke with respect to electron beams and in which a correcting current is supplied to the magnetic lens in synchronism with the scanning by the electron beam so as to obtain uniform beam spots over substantially the entire face of the screen of the cathode-ray tube.

In conventional electron tube devices, for example, in a cathode-ray tube device, the size of a beam spot scanning the front face of the cathode-ray tube has heretofore been a matter of consideration but such attention has not been given to the shape of such beam spot. However, in an apple tube type of color television, a secondary emission material is coated on the screen in suitable relation with respect to three-color fluorescent stripes so that secondary electrons emitted from this secondary emission material can be utilized to detect the position of electron beam. Accordingly, asynchronism of colors and degradation of color purity would result unless an arrangement is made to obtain an electron beam spot which has a fixed diameter over the entire screen face of the cathode-ray tube.

It is however a matter of extreme difiiculty to obtain a spot of small diameter at peripheral portions of the screen of a cathode-ray tube because of the fact that an electron gun and a deflecting yoke have their characteristic astigmatism. Such difliculty is especially marked in an apple tube type of color television in which considerably large current is required to obtain a bright picture. In this connection there is a Langmuirs formula 3,504,21 l Patented Mar. 31, 1970 where:

current density of a beam spot on the screen peak current density at the cathode face Vaccelerating voltage kBoltzmans constant T-absolute temperature at the cathode face 0-half angle when viewed from the spot towards the beam As will be apparent from the above Langmuirs formula, pc and T have fixed values and therefore sin 0, must have a large value in order to obtain a large current density ,0 of the beam spot on the screen. This leads to a requirement that the electron beam at the main lens of the cathode-ray tube must have a large diameter. The manner of beam deflection in cathode-ray tubes for television is such that electromagnetic deflection by the deflecting yoke is generally utilized to deflect the electron beam having just passed through the main lens. However, the greater the electron beam diameter at this position, the more the electron beam is affected by non-uniformity of the magnetic field established by the deflecting yoke and thus the spot on the screen is subjected to a considerably great degree of astigmatism as it moves towards peripheral portions of the screen. Due to such objectionable phenomenon, the deflecting yoke is designed to have the least possible astigmatism but complete elimination of such astigmatism is a matter of difliculty. When, for example, a deflecting yoke generally used in commercially available black-white televisions is used with an electron gun which makes a spot having a visible diameter of 0.35 mm. at an accelerating voltage of 20 kv. and a beam current of 300 a, the spot diameter may sometimes vary to an extent that the spot diameter at peripheral portions of the screen is three to five times the spot diameter at the central portion of the screen. Thus the prior electron beam control device has been defective in that, while it is possible to obtain a beam spot of small diameter at the central portion of the screen, the beam spot has a greater diameter at peripheral portions of the screen and is deformed in its shape with the result that color purity of picture is degraded and it is impossible to obtain a sharp image.

It is therefore the primary object of the present invention to provide a novel and improved electron beam control device which can completely eliminate the defects of the prior device as described above.

The electron beam control device according to the pres ent invention is so effective that astigmatism due to the electron gun and astigmatism due to the deflecting yoke can simultaneously be corrected. Therefore any need for the correction of astigmatism due to the deflecting yoke priorly encountered in this type of device is completely obviated and as a result a deflecting yoke of small size and light weight can satisfactorily be used for the service. Capability of obtaining a beam spot of small diameter over the entire screen face is another advantage, since the beam spot can be corrected in synchronism with an electron beam deflected by a deflecting yoke and therefore it is possible to effect an improvement in color purity of picture and to obtain a sharp image.

Other objects, advantages and features of the present invention will become apparent from the following description with reference to the accompanying drawings, in which:

FIG. 1a is a diagrammatic view showing the basic structure and operation of a magnetic lens consisting of four electromagnetic poles;

FIG. 1b is a diagrammatic view showing the basic structure and operation of an electrostatic lens consisting of four electrodes;

FIG. 2a is a diagrammatic view showing an arrangement of an embodiment of the electron beam control device according to the invention used with a cathode-ray tube;

FIG. 2b is a sectional view taken on the line bb in FIG. 2a;

FIG. 3 is a sectional view of another embodiment according to the invention;

FIG. 4 is a block diagram of one form of a circuitry for bringing an electron beam deflection system in operation in synchronism with a current flowing through the magnetic lens consisting of four electromagnetic poles;

FIGS. 5, 7, 8a and 8b are detail views of circuits shown in the block diagram of FIG. 4;

FIGS. 6a and 6b are graphic illustrations of various waveforms appearing at terminals d, c, f, g, d, e, e, f, g and h in FIG. 5;

FIG. 9 is a schematic view showing positions of spot measurement on the screen face of a cathode-ray tube;

FIG. 10 is a schematic illustration of the shape of spots at positions shown in FIG. 9 when no correction is applied thereto; and

FIG. 11 is a schematic illustration of the shape of spots at these positions when correction is applied thereto by use of two magnetic lenses each consisting of four electromagnetic poles according to the invention.

Referring first to FIG. la showing the basic structure and operation of a magnetic lens consisting of four electromagnetic poles, an electron beam having a sectional shape as shown by 1 travels in the positive direction Z. The magnetic lens includes a correcting coil 2, four electromagnetic poles 3 and control current imput terminals 5. In this arrangement, magnetic field distribution is as shown by flux lines 4. Suppose now control current is made to flow through the correcting coil 2 in a direction shown by the arrow. By this current flow, those electrons which are in the vicinity of points 6 and 8 in the electron beam section 1 are deflected outwardly away from the center of the electron beam section 1, while those electrons which are in the vicinity of points 7 and 9 are deflected inwardly towards the center of the electron beam section 1. It will be understood that, in this manner, the so-called circular electron beam is deformed by the magnetic lens consisting of four electromagnetic poles into an elliptical shape whose major axis extends in the direction of the Y axis. By reversing the direction of current flow through the coil 2, the circular electron beam can likewise be deformed into an elliptical shape whose major axis extends in the direction of the X axis. It will also be known that the rate of deformation of the circular beam can freely be varied by suitably varying the magnitude of control current flowing through the coil 2.

In FIG. 1b showing the basic structure and operation of an electrostatic lens consisting of four electrodes, an electron beam having a sectional shape as shown by 1' runs in the positive direction Z. The electrostatic lens includes four electrodes 3 and control voltage applying terminals 5. Suppose now voltages +V and V are applied across these electrodes 3 as shown. By this application of control voltage, those electrons which are in the vicinity of points 6 and 8 are deflected outwardly away from the center of the electron beam section 1', while those electrons which are in the vicinity of points 7' and 9' are deflected inwardly towards the center of the electron beam section 1. It will be understood that, in this manner, the so-called circular electron beam is deformed by the electronstatic lens consisting of four electrodes into an elliptical shape whose major axis extends in the direction of the Y axis. Likewise by reversing the polarity of voltage applied across the electrodes 3, the circular electron beam can be deformed into an elliptical shape whose major axis extends in the direction of the X axis. It will also be known that the rate of deformation of the circular beam can freely be varied by suitably varying the magnitude of control voltage applied across the electrodes 3'.

As described above, there are two types of electron beam control lens, that is a magnetic lens consisting of four electromagnetic poles and an electrostatic lens consisting of four electrodes, and there is not any appreciable diiference between their electron beam controlling operations. The following description will be directed to an electron beam control device employing the magnetic lens as a beam control means. The magnetic lens may more advantageously be used than the electrostatic lens when a lens of shortened length is desired with relations to the velocity of electron beam.

FIG. 2 shows a diagrammatic arrangement of an embodiment according to the present invention when used with a cathode-ray tube, FIG. 2a being an axial sectional view and FIG. 211 being a sectional view taken on the line b-b in FIG. 2a. The cathode-ray tube includes a cathode 10, a grid 11, a first anode 12 and a second anode 13, and the wall of the cathode-ray tube is designated by 14. A deflecting yoke is designated by 15, while the magnetic lens consisting of four electromagnetic poles according to the invention is designated by 16. It will be seen that the magnetic lens 16 for the correction of astigmatism can be disposed at any position in a range 1 between the cathode 10 and the deflecting yoke 15. It will however be understood that the magnetic lens 16 consisting of the four electromagnetic poles may preferably be disposed at a position at which the velocity of electron beam is relatively slow, that is, at a position closer toward the cathode 10 in order to minimize the amount of correcting current and to provide ease of correction.

FIG. 3 is a sectional view of another embodiment according to the present invention, in which like. reference numerals appearing in FIGS. 1 and 2 are used to denote like parts. In this embodiment, masses of magnetic material forming the electromagnetic poles are embedded in the electrode such as the grid or anode since the electron beam can more effectively be controlled as the electromagnetic poles of the magnetic lens are disposed closer toward the electron beam. In FIG. 3, the masses of magnetic material are shown as embedded in the grid of a cathode-ray tube.

The angular position (the maximum angular position being at an angle. of 45) of the magnetic lens consisting of four electromagnetic poles as described above and the magnitude and direction of correcting current flowing through the magnetic lens may be suitably regulated for thereby effecting the most desired correction of astigmatism which is characteristic of an electric gun and at the same time for imparting to the electron beam before being guided into the deflection system such astigmatism as will be exactly opposite to the astigmatism which is developed by the deflection system. In this manner, it is possible to obtain a circular spot of substantially uniform size everywhere on the screen of a cathode-ray tube or an eilliptical spot if so desired.

The foregoing description has been directed to a case in which one magnetic lens consisting of four electro magnetic poles is used for the electron beam control. In this case it is necessary, in order to effect satisfactory correction, to cause the magnetic lens to rotate within an angle of rotation of 45 as the position of the spot successively varies. It is true that the magnetic lens may be fixed at the optimum angular position within an allowable limit of astigmatism imparted to the beam spot, but such optimum fixed angular position may vary deending on individual cathode-ray tubes since the astigmatism imparted to spots may vary depending on electron guns, deflection systems and other elements of cathoderay tubes. This leads to a defect that complex regulation of angular positions becomes necessary and the accuracy of correction is thereby lowered. This defect can be overcome by combining two magnetic lenses of the type described in a manner that they are fixed at positions at which they are rotated through an angle of rotation of 45 relative to each other. By so arranging it becomes possible to correct any astigmatism by mere regulation of the magnitude and direction of correcting current flowing through the coils of the magnetic lenses consisting of four electromagnetic poles, with the magnetic lenses fixed in position. It will easily be understood that more than two of such magnetic lenses consisting of four electromagnetic poles may be used as desired.

FIG. 4 is a block diagram of one form of a circuitry for bringing an electron beam deflection system in operation in synchronism with a current flowing through the magnetic lens consisting of four electromagnetic poles. A portion 23 surrounded by dotted lines in FIG. 4 represents a deflection circuit system heretofore commonly employed in a television receiver and includes a vertical deflection sweep oscillator 18, a vertical deflection power circuit 19, a horizontal deflection sweep oscillator 20, a horizontal deflection power circuit 21 and a deflecting coil assembly 22. The circuitry further includes a correcting current generator unit 24 and a magnetic lens 25 consisting of four electromagnetic poles according to the invention, and signal input for the synchronization with beam deflection is supplied to a terminal 17.

In FIG. 5 there is shown a detail view of the structure of the deflection circuit system 23 shown in FIG. 4 and like reference numerals are used to denote like parts. In FIG, 5, the vertical deflection sweep oscillator 18 includes an integrator 26 and a vertical multivibrator and saw tooth wave generator 27, while the horizontal deflection sweep oscillator 20 includes a dilferentiator and an automatic horizontal frequency control circuit (AFC)31. The vertical deflection power circuit 19 includes a tube V a vertical deflection power transformer 28 and a synchronizing signal lead-out winding 29, while the horizontal deflection power circuit 21 includes tubes V V and V a horizontal deflection power transformer (horizontal flyback transformer) 32, a synchronizing signal lead-out winding 33 and a horizontal linearity control section 34. The deflecting coil assembly 22 in FIG. 4 is represented by a vertical deflecting coil 22' and a horizontal deflecting coil 22" in FIG. 5. Synchronizing signal lead-out terminals d, e, f and g are provided to attain synchronization between the vertical deflection system and the correcting current. Likewise, synchronizing signal lead-out terminals d, e, f, g and h are provided to attain synchronization between the horizontal deflection system and the correcting current.

Signal waveforms derived at the above-described terminals are shown in FIG. 6, in which like symbols represent those waveforms appearing at the terminals having like symbols in FIG. 5. The phase of the signals 1 and 1" may be reversed as shown or their amplitude may be varied by suitably manipulating variable resistor portions 29 and 33' of the respective windings 29 and 33. Signal Waveform appearing at a terminal e" may suitably be varied by manipulating the horizontal linearity control section 34. Any one of the synchronizing signals derivable from the above-described terminals can be utilized to generate the correcting current, as will be described in detail below with reference to FIG. 7.

FIG. 7 shows the structure of a vertical correcting current generator forming part of the correcting current generator unit 24 shown in FIG. 4. Though the correcting current generator unit 24 also includes therein a horizontal correcting current generator therein, no descrip tion will be given herein because this horizontal correcting current generator has a structure entirely the same as that of the vertical correcting current generator except that the former derives its synchronizing signal input from the horizontal deflection power circuit 21 whereas the latter derives its synchronizing signal input from the vertical deflection power circuit 19. These vertical and horizontal correcting current generators are arranged to be controlled independently of each other, and the vertical and horizontal correcting coils 2 shown in FIG. 1 are coiled about the same iron core having the electromagnetic poles 3 of the magnetic lens. Reference numerals 35 and 36 in FIG. 7 designate vertical synchronizing signal input terminals which are connected, for example, to the terminals d and e in FIG. 5, respectively. Phase splitters 37 and 37 split the respective input signal wave forms d and e into signal waveforms of opposite phases to each other as shown. Variable resistors 38 and 38' are provided to regulate the correcting current waveforms andoutputs therefrom are supplied to an adder 41 by way of respective terminals 39 and 40. A phase splitter 42 is connected to the adder 41 so that the output from the phase splitter 42 can be supplied through directcurrent component cut-ofl condensers 43 and 43 to grids of a double cathode tube V disposed in the form of a push-pull circuit 45. The push-pull circuit 45 includes grids biasing resistors 44 and 44' and a correcting coil 46 of the magnetic lens consisting of four electromagnetic poles. This correcting coil 46 is doubly coiled about the iron core having the electromagnetic poles 3 and is adapted to supply a voltage +B from its middle point. A source of power supply 47 and a variable resistor 48 are provided to variably bias the grids of the tube V It will thus be understood that satisfactory correction of beam spots can be eifected by suitably regulating the variable resistors 38, 38 and 48 in the circuitry.

FIG. 8 shows another form of synchronizing signal waveform converter. In FIGS. 8a and 8b, block 50 and 53 represent an integrator and a phase splitter, respectively. In such an arrangement, the signal waveform f in FIG, 6, for example, may be supplied to an input terminal 49 of the integrator 50 and its output terminal 51 may be connected to the terminal 39 shown in FIG. 7. The signal waveform g in FIG. 6 may be supplied to an input terminal 52 of the phase splitter 53 and its output terminal 54 may be connected through the integrator 50 to the terminal 39 shown in FIG. 7.

Any detailed description with regard to the horizontal correcting current generator will be unnecessary since its structure is entirely same as that of the vertical correcting current generator as described above with reference to FIG. 7. Therefore a preferred method of supplying synchronizing signal waveforms derived from the horizontal deflection {power circuit 21 in FIG. 5 will only be 'briefly described herein. In supplying the synchronizing signal waveforms to the horizontal correcting current generator, the synchronizing signal waveforms d and h in FIG. 6 may be supplied to the terminal 35, the synchronizing signal waveforms e' and e" may be supplied to the terminal 36, the synchronizing signal waveform f may be supplied through the integrator 50' (FIG. 8) to the terminal 39, or the synchronizing signal waveform g may be supplied through the phase splitter 53 and the integrator 50 to the terminal 39. It will thus be understood that, by employing a suitable waveform converter, any of these synchronizing signal waveforms can be utilized as an input to the correcting current generator.

FIG. 9 is a schematic view showing positions of spot measurement on the screen face of a cathode-ray tube. The screen face of the cathode-ray tube is designated by 55 and positions of spot measurement on the cathoderay tube screen 55 are designated by 56, 57 64. Shapes of spots at these positions 56, 57 64 when no correction is applied thereto are illustrated in FIG. 10, in which spot shapes corresponding to the positions 56, 57 64 i611 FIG. 9 are designated by dashed numerals 56', 57'

These spot shapes can for example be corrected to corresponding spot shapes 56", 57" 64" as shown in FIG. 11 when the electron beam is corrected by use of two magnetic lenses consisting of four electromagnetic poles each according to the invention. In FIGS. 10 and 11, a vertical solid line represents the boundary between a set of three-color (red, green and blue) fluorescent stripes and an adjacent set of three-color fluorescent stripes, and vertical dotted lines in each stripe set represent the boundaries between red, green and blue fluorescent stripes. Table 1 below shows current values supplied to the correcting coils of the magnetic lenses consisting of four electromagnetic poles to eflect the spot shape correction as shown in FIG. 11.

The current values in Table 1 are merely shown by way of example and it is to be understood that current values to be supplied to the correcting coils vary in each individual cathode-ray tube.

Further it will be understood that the electrostatic lens is also capable of making similar operation when it is used in lieu of the magnetic lens referred to above.

What is claimed is:

1. An electron beam control device for use in conjunction with a cathode-ray tube having at least a cathode for generating an electron beam and a deflection system for deflecting the electron beam comprising:

at least two corrective electron lens assemblies coaxially aligned with the axis of said cathode-ray tube and positioned between said cathode and the deflection system with relative angular displacement between any two poles in each corrective lens assembly being between and 45 measured about the common axis and with each corrective electron lens assembly operatingly producing a four-pole field for correcting astigmatism of the electron beam; and

lens actuating means for independently actuating said two corrective electron lens assemblies with respective field producing signals derived from the respective horizontal and vertical scanning signals of the deflection system in a manner such that each corrective electron lens varies the field intensity and polarity of its four-pole field in a synchronized relation to the scanning of the electron beam as it is deflected by said deflection system to thereby minimize astigmatic effects and maintain optimum focus throughout the area scanned by the electron beam.

2. An electron beam control device according to claim 1 wherein the corrective electron lens assemblies are embedded in one of the electrodes of the cathode ray tube.

3. An electron beam control device according to claim 1, wherein said two corrective electron lens assemblies are aligned with the relative angular displacement of the four poles of one lens measured with respect to the four poles of the other lens about the common axis being substantially 45.

4. An electron beam control device according to claim 3, wherein:

each of said two corrective electron lens assemblies comprise four electro-magnetic poles positioned in equiangularly spaced relation about said common axis of said electron lens assemblies for operatingly producing a four-pole electro-magnetic field, and coil means for operatively magnetizing circumferentially adjacent two poles of said electro-magnetic poles in an opposite direction alternatively; and

said lens actuating means comprises means for applying a control current to each of the coil means of both said electron lens assemblies, and means for varying the polarities and intensities of the control currents applied to the respective coil means in synchronized relation with the scanning of the electron beam, respectively, in a manner such that each of said electromagnetic lens assemblies varies its four-pole electro-magnetic field independently of the other.

5. An electron beam control device according to claim 4 wherein the electro-magnetic poles of both corrective electron lens assemblies have respectively a pole piece which is embedded in at least one of the tube electrodes located between said cathode and the deflection system.

6. An electron beam control device according to claim 3, wherein:

each of said two corrective electron lens assemblies is formed of four electro-static electrodes positioned in equiangularly spaced relation about said common axis of said electron lenses for operatingly producing a four-pole electro-static field; and said lens actuating means comprises means for applying a control voltage to circumferentially adjacent two electrodes of said electro-static electrodes of each of the electron lens assemblies so as to render the poles alternately of opposite polarity, and means for operatingly varying the polarity and intensity of the respective control voltages applied to the respective electro-static electrodes of both the electron lens assemblies in synchronized relation with the scanning of the electron beam, respectively, in a manner such that each of said electron lens assemblies varies its four-pole electro-static field independently of the other.

7. An electron beam control device according to claim 6 wherein the electro-static electrodes of both electron lens assemblies are embedded in at least one of tube electrodes located between said cathode and the deflection system, said electro-static electrodes being insulated from said tube electrodes.

8. An electron beam device comprising:

a cathode for generating an electron beam and a deflection system for deflecting the electron beam;

at least two corrective electron lens assemblies for producing two corrective fields for deflecting electrons inwardly toward the axis of said beam in a direction parallel to a first axis lying in a plane perpendicular to said axis at said beam and outwardly away from the axis of said beam in a direction parallel to a second axis lying in said plane and perpendicular to said first axis, said corrective lens assemblies being aligned coaxially with the axis of said beam and with the first and second deflection axis of one of the corrective lens assemblies crossing the first and second deflection axis of the second corrective lens assembly at some predetermined angular displacement; and

means for controlling the intensity and polarity of the corrective field at each of said corrective lens assemblies in synchronism with the scanning of the deflection system.

9. An electron beam device according to claim 8 in which said corrective lens assemblies are disposed with relative angular displacement to each other of substantially 45 about the axis of said beam.

References Cited UNITED STATES PATENTS 3,371,206 2/1968 Takizawa 313-83 X 2,919,381 12/1959 Glaser 313-84 X 3,071,707 1/ l963 Schleich 31384 3,150,284 9/1964 Comeau 3l384 X JAMES W. LAWRENCE, Primary Examiner V. LAFRANCHI, Assistant Examiner US. Cl. X.R. 31531 

